The present invention relates to a radio selective-calling receiver which in particular maintains stable operation with a sufficient power supply.
Description of the Related Art
Generally, a conventional radio selective-calling receiver operates with one dry battery and has an intermittent operation in order to extend battery life, and only at the time when the data corresponding to the ID of a receiver owner are received, a radio section is switched on and the data are taken in. However, a controller of the radio section always operates to control the operation timing of the radio section. To operate the controller, at least about 2 volt is needed in the current available CPU and so forth, and to supply the voltage, for example a step-up transformer type DC/DC converter as shown in FIG. 1 is used.
In FIG. 1, a transistor 511 is switched on or off by an oscillator 512 and at the "on" state of the transistor 511, the energy supplied from a battery 510 is stored in a coil 513 and when the transistor 511 is turned "off", the energy is supplied to a capacitor 515 via a diode 514. With these operations, at the both terminals of the capacitor 515, the step-upped output voltage Vout is generated.
In this case, by the switching operation of the transistor 511, the switching noise as shown in FIG. 2 is included in an output wave form and the higher harmonic waves of this switching noise is radiated and has a bad influence on the characteristics of the reception sensitivity and so forth.
For example, the Japanese Patent Laid-Open Publication No. HEI 6-53883 discloses the radio selective-calling receiver which eliminates of the bad influence of the switching noise of DC/DC converter as shown in FIG. 3.
FIG. 3 is a block diagram showing the construction of the conventional radio selective-calling receiver. In FIG. 3, the radio selective-calling receiver provides a radio section 501 demodulating received signals, a controller 502 which controls intermittently the operation of the radio section 501 and decodes the demodulated signals from the radio section 501 and outputs the signals controlling on/off of a DC/DC converter 503, a primary battery 504 supplying power to the radio section 501 and a secondary battery 505 supplying power to the controller 502. The DC/DC converter 503 is switched on at right before switching on the radio section 501 and converts the power of the primary battery 504 from DC to DC and charges the secondary battery 505 and supplies the power to the controller 502. An operating section 506 implements the interruption to the controller 502 by the operation of a user.
Next, the operation is explained. The radio section 501 amplifies and demodulates the received signals and supplies the demodulated signals to the controller 502. The controller 502 decodes the demodulated signals and also controls the radio section 501 and the on/off controlling of the DC/DC converter 503, and the DC/DC converter 503 is switched on at right before switching on the radio section 501 and charges the secondary battery 505 and supplies the power to the controller 502. At the time of "off" of the DC/DC converter 503, the secondary battery 505 supplies the power to the controller 502. The primary battery 504 supplies the power to the radio section 501 and the DC/DC converter 503. As mentioned above, the power supply to the controller 502 is implemented by the secondary battery 505 and the charge of the secondary battery 505 is implemented by the DC/DC converter 503 at right before switching on the radio section 501, therefore the bad influence of the switching noise of the DC/DC converter 503 is possible to be eliminated.
FIG. 4 is a timing chart showing the operation of the radio section 501 and the DC/DC converter 503 of the conventional radio selective-calling receiver using POCSAG (Post Office Code Standardization Advisory group) format. FIG. 5 is a timing chart showing expanded the "A" part of the timing chart of FIG. 4, this shows the change of the output voltage of the secondary battery 505. As shown in FIG. 4, the operation timing of the DC/DC converter 503 is completely different from the operation timing of the radio section 501, as shown in FIG. 5 (2), the DC/DC converter 503 is switched on for a short period at right before switching on the radio section 501 and implements the charge of the secondary battery 505 and the power supply to the controller 502, and at the time of "off" of the DC/DC converter 503, the secondary battery 505 supplies the power to the controller 502 with this charged energy.
The conventional radio selective-calling receiver has the construction stated above. As shown in FIG. 5 (3), at a point "a" the DC/DC converter 503 is switched off and the radio section 501 is switched on and the output voltage of the secondary battery 505 is gradually decreased by the consumption current of the controller 502. This corresponds to the voltage change showing between points "a" and "b" in FIG. 5 (3). Until again switching on the DC/DC converter 503, if the consumption current of the controller 502 does not change, the gradually decreasing output voltage of the secondary battery 505 does not become below the minimum operating voltage Vmin of the controller 502. However, at the case that a user operates the receiver at the point "b", by the rapid increase of the consumption current of the controller 502, the output voltage of the secondary battery 505 decreases greatly and becomes below the minimum operating voltage Vmin of the controller 502 at a point "c", the problem stopping the operation of the controller 502 occurs.
The operation timing of the DC/DC converter 503 is completely different from the operation timing of the radio section 501, therefore there is a problem that a control signal SW only for the DC/DC converter 503 is needed to be provided.
Moreover, because of the charging time of the secondary battery 505 is short, there is a problem that the restoring time of the terminal voltage of the secondary battery 505 to a sufficient voltage driving the controller 502 takes long.